Here’s a really cool study of YouTube videos from Social Bakers.
The most commonly viewed videos are 31–60s long (32% of all views)
The shortest videos are generally the least commonly watched
Videos longer than 5 minutes are the next least commonly watched, but that does not hold true for all industries.
Despite there being fewer videos in the 31 to 60 second range than in the 61 to 90 second range, the former category took on more views than the latter.
via YouTube For Smart Social Marketers | Social Media Statistics & Metrics | Socialbakers.